


Fishsticks

by musegaarid



Category: Supernatural
Genre: Adoption, Alternate Universe, Anal Fingering, Babies, Breeding, Cloacal Fingering, Dirty Talk, Fluff and Smut, M/M, Nipples, No mpreg, Rimming, Sappy Ending, Telepathy, Weird Biology, fish sex, mermaid au
Language: English
Status: Completed
Published: 2018-11-04
Updated: 2018-11-04
Packaged: 2019-08-17 11:13:42
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,952
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16515305
Author URL: https://archiveofourown.org/users/musegaarid/pseuds/musegaarid
Summary: From the waist down, Mer!Cas and Mer!Dean are fish, which means that they don’t have dicks. That doesn’t stop them from having sex and making babies, but it does mean they might get the order a little mixed up.





	Fishsticks

Just as Leader Ellen took her place at the front, Castiel drifted into the rear of the community grotto. He had attended two Announcements a year for every one of his twenty-six years, so he was not expecting that this one would be of any particular interest either. He only hoped that Leader Ellen’s speech would be shorter and less pretentious than Leader Michael’s had been. 

“Howdy, merfolk,” Ellen began, projecting her thoughts for all to hear. Her tone had its usual no-nonsense feel. “Thank you all for attending this Announcement. I won’t bore you by explaining the history of this event or its purpose, since you all know why we’re here. Instead, I’m going to come right to the point. After carefully considering all of the eligible men of our school, the Council has decided on a mer who is quiet, thoughtful, patient, and serious. Though he might not be considered one of our finest hunters, he is maybe the best craftsman we’ve got, and we’d be better off with fewer blockheads around anyway.” She looked pointedly at someone in the middle of the crowd, but Castiel couldn’t see who it was. “So, our Candidate for this Announcement is Castiel. Where you at, kid?”

Jerking his tail in shock, Castiel was suddenly propelled a few feet upward. Ellen gestured him forward and he went reluctantly, feeling every mer’s eyes upon him and avoiding them all.

He took his place next to Ellen. “I...” he began, unsure what to think or what feelings he was even projecting. Extreme reluctance for one. “I...”

“Okay, Castiel,” interrupted Ellen. “This is an honor, your sacred duty, yadda, yadda, yadda. You gonna do this for us or what?”

“I...” repeated Castiel. He looked at Ellen’s fond expression and then down at the sand, wishing his hands were occupied. He looked out at the expectant crowd and swallowed. Though he wasn’t at all sure he could do this, he should at least try. It really was his duty and nearly everyone had to do it eventually. Vaguely he wondered if there had ever been a Candidate who failed, as it was very likely that he would. 

“I will,” he thought quietly, hoping he wasn’t lying to her. He hadn’t put enough effort in for the thought to travel far, but Ellen heard it and nodded. 

“Good,” announced Ellen. “You all know the drill, then. Every mermaid between the ages of eighteen and thirty will go to the breeding grounds sometime this week to lay her eggs, unless they had the same daddy as Castiel.” She turned to him. “It was Chuck, wasn’t it?”

Castiel nodded.

“Okay, anyone from Chuck’s clutch stay clear, but the rest of you have until Friday to lay your eggs. Castiel will go by on Saturday to fertilize them and you’d best be giving him his privacy. If you’re thinking you might want one of Castiel’s fry, you come on by and see me in the next three months and I’ll put you on the list. Thanks everyone for stopping by.”

This was clearly a dismissal, so everyone began to swim for the exits to continue their day, but Castiel was frozen in place. It was such a big responsibility to father children for the community and he didn’t want to let them down, but at the same time, he knew he couldn’t perform. What would happen when he wasted all those eggs. Would they be angry enough to exile him to the dark waters beyond?

A friendly hand on his shoulder jostled these unhappy thoughts out of his head and he turned to look into the green eyes of Dean Winchester, Clutch Michael. Dean was the school’s star hunter and biological son of their last Leader, though he’d been raised by John and Mary Winchester. The three shark skins hanging in his home attested to his prowess, and he’d been a Candidate years ago – practically the moment he was old enough. Castiel wasn’t tracking the lives of Dean’s clutch, exactly, but he did know all their names and what couples were raising them, and they all seemed to be growing up as attractive and strong as their clutch father. Of all his children, Dean seemed particularly close to young Ben Braeden and his widowed mother, Lisa.

“I wondered when it would be your turn, Cas,” Dean grinned. His mental tone was mostly cheerful but with a hint of melancholy that Castiel did not understand. “But I wish they’d waited a bit longer. Can’t take one of your fry without a partner.”

“You’d want one of my fry?” asked Castiel, bewildered. They’d never been especially close friends, but while he paid a lot of attention to the hunter, he’d never thought the regard was mutual. When he had thought about Dean’s future life, he figured that Dean would choose the fry of one of the better hunters, like Benny or Cole, not a basket weaver like himself. And raise them with one of the school’s beauties. 

“Sure, man,” said Dean. His words felt earnest, but also like he was trying to hide how earnest he felt. “You’re smart and good-looking. Who wouldn’t want a smart and good-looking kid?” He laughed a bit self-consciously. “Always thought I’d try to get one of yours and one of Sammy’s, though he’s still got at least four more years to wait, what with the whole family thing and me going six years ago.”

Castiel blinked. He supposed it had already been ten years since his own brother Gabriel had been called upon to do his duty. Having a bunch of short and hyperactive mers was good for the school’s genetic diversity, but probably hell on their fifth grade teacher. 

“Sam is of Clutch Lucifer, is he not? That is a powerful line.”

Dean shrugged. “Yeah, but that’s not why I want to raise his kid. And Sam isn’t much like his clutch father, thank Poseidon. He’s steady, knows what he wants, and works hard. That’d be a good kid to have. Might even have tricked someone into being my partner by then.” He winked. “Don’t think it’ll happen in the next three months, though...”

Castiel only had low-level telepathy, like most mers, but he could sense Dean’s sadness. “Do not worry. I am very unlikely to produce fry, so you will not be missing out on anything.”

“Why can’t you?” asked Dean with a frown. 

Unable to hold Dean’s eye, Castiel looked back down at the sand and twisted his hands together. “I... don’t know how.”

“It’s just like doing it at home, dude! Nothing special about doing it over some eggs. What’s to know?”

He drifted lower to the ocean floor hoping for some kind of escape from the conversation. “I _don’t_ know _how_ , Dean,” repeated Castiel, with a mental growl. 

“Oh!” Dean rubbed the back of his neck nervously. “Oh, you haven’t... I mean, that’s, that’s fine you know. Not judging or anything. Just, ah, surprised. I kinda thought everyone, you know, cleaned the pipes every now and then.”

Castiel scowled. “You can say ‘spawned.’ It’s not a dirty word.”

“Well, okay, it’s fine if you haven’t _spawned_ before,” insisted Dean, irritable in his embarrassment. “Doesn’t mean you can’t.”

“And how do you propose I start, then?” demanded Castiel a second before realizing that he actually didn’t want Dean to answer that question.

Dean put up his hands defensively. “Whoa, I’m not really... Look, I could help. If you want me to. You know, since I’ve, uh, done it before.”

Swimming closer, Castiel eyed Dean closely. “You want to help me spawn,” he thought flatly.

In the water, Dean’s faint blush seemed to tint the skin of his cheeks a dark blue. “Not _help_ necessarily. Just, you know, talk you through it. Give you pointers. That sort of thing. I could turn around so it’s not, you know, weird.”

“Weird,” repeated Castiel. This whole conversation was ‘weird.’ But he’d be lying if he said he’d never thought about it before. And perhaps he did need the help. He wouldn’t spontaneously learn by Saturday. “All right. As long as it’s not ‘weird.’”

Dean sighed and a stream of water flowed through his gills. His thoughts were tinted with panic and something else that Castiel couldn’t identify. “Okay. All right, then. I guess I’ll see you there.” 

Before Castiel could reply, Dean was gone with a single undulation of his muscular tail, leaving Cas in the huge, empty grotto alone and wondering what he had gotten himself into.

***

All week Castiel tried to spawn by himself. He read biology tablets at the library, which were both unhelpful and boring. He also read romance novels, which were less boring, but equally unhelpful. All the mermen in the books seemed to be able to spawn on command. In his seaweed bed at night, he prodded at his abdomen, wondering how to make his milt come out. This was decidedly not something he felt comfortable talking to his family about. His parents, Naomi and Zachariah, were strict and old-fashioned, and they believed that spawning was for procreation only. They were distantly proud and assumed he would know what to do when the time came, or at least that’s what he gathered from their vague metaphors about the pull of the tides. And Gabriel would ridicule him until the end of time if he knew of Castiel’s problem. No, it seemed like Dean was really the only person who could help. 

***

It was with some trepidation that he approached the breeding grounds on Saturday, noticing the bubble nest that had been assembled to hold the eggs. Dean was looking into it thoughtfully, until he noticed Castiel’s approach.

“Geez, _there_ you are!” Dean thought at him. Castiel picked up on his impatience, uneasiness, and some measure of relief, as well. “You’re slower than a seahorse in the morning, I swear!”

“I apologize if I kept you waiting...” he began, but Dean waved off his explanation. 

“It’s fine. Let’s, just, do this.”

Castiel nodded, uncomfortable, but determined. “What do we do?”

“Well, _I_ am going behind that rock.” Dean pointed to a boulder off to one side of the breeding grounds that would provide shelter for the hundreds of fry that would theoretically be produced from this spawning. But the ocean is a cruel place and perhaps only a dozen would survive long enough to be adopted by loving families in the school. By breeding about twelve children twice a year, the school was able to replace the roughly equal number of adults who died each year, and keep the community in balance with their surroundings. If there were too many merpeople in the school, they would deplete their stocks of food through overfishing and overforaging. Too few meant that they would lose the advantage of safety in numbers and be picked off individually by bigger predators until the school was decimated. This method of reproduction kept their population in check while preventing inadvertent incest and inbreeding, or leaving a single family to raise twelve fry on their own. 

“Okay,” Dean thought loudly, once he was in place. “I’m going to tell you what to do from over here and you just do your thing. I’m looking in the other direction and should be far enough away that I can’t pick up on your, ah, feelings, or whatever.”

“I understand,” Castiel projected back, looking down at the thousands of mixed-up jewel-colored eggs below. His potential children.

“Right,” said Dean. “So, first things first, you’ve gotta get in the mood. It doesn’t work if you’re not turned on.”

Ah, so that’s what he’d been missing in his solo efforts. “How do I get turned on?” he asked.

“Well, you’ve gotta think of something sexy. Like... try to imagine someone who you think is really hot. Ooh, imagine Amelia without her seashells on!”

Even at this distance, Castiel could sense Dean’s lascivious interest in the mermaid. He frowned. “That is highly disrespectful,” he retorted. “Besides, Amelia is being courted by my clutchmate, Jimmy.”

“Oh, sorry,” Dean replied, contritely. “I didn’t know. I do try not to think about partnered people like that.”

“You shouldn’t think about anyone like that without their permission.”

Discomfort radiated through the water. “I think asking would make them a lot more uncomfortable,” said Dean finally. 

Castiel thought about it for a moment. Would he want someone to ask him if they could fantasize about him sexually? _Had_ anyone ever fantasized about him without his knowledge? Which was worse? “Perhaps you are right,” he conceded. “It would be... awkward to ask.”

“Yeah,” snorted Dean, “No kidding. Then think about someone single that you find attractive. Or, uh, _do_ you find anyone attractive? Just yes or no is fine, you don’t hafta tell me their name or anything,” he hastened to add.

“Yes,” Castiel intoned. “There is someone I find attractive.”

“Good, okay.” Dean’s mental voice sounded strained. “So, like, think about being close to that person. Imagine touching their shoulders, their waist, their fins. Picture yourself running your fingers down their cheek and leaning in for a kiss. It starts off pretty tame, but then they part their lips and things get intense fast. You’re winding your hands in their hair while they wrap their tail around yours to keep you close. You picturing this, Cas? Does it make you feel sexy?”

Castiel closed his eyes, imagining the scenario Dean described. How his body would move against Dean’s. How he would run his hands over Dean’s gunmetal gray scales and trace where they shaded to dark red on his ventral side. How those plush, warm lips would feel pressed against his own. 

“I... yes?” he sent distractedly. “Now what?”

“Now you get physical. Run your hands over your chest, down to that sensitive area where your scales start, then back up. Start, uh, rubbing and pinching your nipples. Do whatever feels good, man. You ever played with your nips before? I bet you haven’t. It’s better when someone else is there to suck and bite them, just on the good side of too much, but it still feels damn good when you squeeze them yourself.”

Castiel’s mind was awash in new sensation. Just pinching his nipples wasn’t enough. There was a fine line of something that seemed promising between not feeling much of anything and an uncomfortable sting, but he couldn’t quite find it until he tried twisting instead. That sent a line of heat rocketing through his core. Water flooded his open mouth as he found the balance between ecstasy and pain. 

“How’s it going?” asked Dean tentatively after a few moments.

“It is... gratifying,” Castiel replied. “My left nipple is more sensitive than the right. I’m enjoying twisting it and rolling it through my fingers.”

“Wow, okay.” Dean’s obvious amusement was layered with something darker and heavier that Castiel couldn’t identify this far away. “Good, so you’re probably ready for the next part. You’re gonna move lower and start feeling up the area around your, uh, pee hole. Just, like, relax and massage yourself there. Squeeze around a bit. You’ll know it’s working when you see a drop of milt beading up.”

Running his fingertips along the alternating light and dark blue stripes that decorated his scales, Castiel teased his flesh. Touching the place where waste exited his body was probably unhygienic, but he couldn’t deny that it also felt amazing. 

“ _Dean..._ ”

“Yeah?”

Oh! He hadn’t meant to project that particular thought. “Keep talking,” he demanded, needing a reason to have called the other man’s name.

Dean’s mental voice was somehow deeper and darker when he began to project again. “You getting hot, Cas? Ready to blow your load over those eggs? Make some babies for me? I bet you spray so hard that the folks in town are tasting it for a week.”

The thought was both deeply disgusting and highly erotic. Castiel groaned. A white substance began welling up under his fingers as he rubbed faster.

“I watch you,” admitted Dean finally. “You swam past me last week, and all I could think about was how much I wanted to get my fingers in your pretty hole. Almost crashed right into a fucking wall, I needed to get home so fast. Pretty sure you said something, but Poseidon only knows what it was.”

Listening to Dean’s confession made something clench deep inside Castiel’s body. His hand was a blur over his sensitive cloaca.

“You probably think I’m some kind of dumb meathead, but I swear I’m just distracted when you’re nearby. Another day I was watching you braid seaweed and you put the ends between your lips to hold them. Fuck. I had three fingers in my slit before I even knew where I was. Woulda bust right in the town square if I hadn’t seen Ellen and Jo coming around the corner. I spawned four times that night, thinking about your mouth.”

“Dean!” cried Castiel, frustrated. “I feel _something_ but I can’t... It won’t... I need more!”

“You need my help?” asked Dean. “Want me to put my hands all over you? Milk that gorgeous body?”

“Yes!” 

Dean turned and sped over, cursing when he caught sight of Castiel running his hands over his swollen opening. “Poseidon’s fucking trident, Cas... C’mere.”

He grabbed Castiel’s head and drew him into a searing kiss. 

“Want you so much,” echoed in Castiel’s mind, but it was difficult to hear over his own surprise and desire, and he wasn’t sure if Dean meant to send it at all.

Thinking of Dean’s words earlier, Castiel threaded his fingers into Dean’s hair and wrapped his tail around the other mer without breaking their kiss, although he gasped as Dean’s scales brushed against the hottest and most sensitive part of his body. 

“Gonna make you feel so good, baby,” whispered Dean in his mind as they continued to make out. “Need you to spill for me. Give me the tiny Cas I want so bad. Wanna mate you and raise her up together. If she’s even half as smart as you and has your big, blue eyes, then I’ll be happy.”

Castiel’s brain was on overload. Dean wanted to mate him and start a family? The strongest, most loyal, and most beautiful mer in the whole school? The one who apparently could do heavenly things with his tongue?

“Want that, too,” he managed. “Help me make her for you.”

Dean cursed again and put his hands on Castiel’s waist, lifting him up higher in the water so he could get his full lips around Castiel’s warm nipple. He licked and teased it into peaking in the cool water, then gently nipped at the heated flesh. 

Castiel’s tail curled in shock and delight as he moaned. “Ohh, Dean!”

Continuing his oral assault, Dean lifted his hand to begin pinching and twisting Castiel’s other nipple. “Fuck, I always wanted to suck on these tits,” he thought as his tongue swirled around the brown nub. “I see them every day, just innocently out there, and every damn day thinking how much I want to wrap my mouth around them and pull you in. And your hole... damn. Just winking to the whole ocean like an invitation. Nothing stopping me from getting my fingers in you.”

“Do it,” sighed Castiel. He thought his own ministrations had prepared him for someone else’s touch, but nothing could have prepared him for Dean sinking down another couple of feet and tonguing at his entrance. He’d never even _heard_ of such a thing. It was utterly filthy and the sexiest thing he had ever experienced.

“Dean!” he cried loudly, the name reverberating in his head like an aftershock. His body felt like molten lava as Dean’s hot mouth probed at his most intimate place. 

“Yes, want, taste so good...” projected Dean disjointedly as his tongue traced Castiel’s hole and delved inside. “Tell me before you blow. Can’t waste a drop. Gotta flood these eggs – fatten ‘em up with your fry.” 

Castiel’s head fell back. He felt simultaneously light enough to bob to the surface and heavy enough to sink into the silt. Why the thought of making children was so invigorating now he couldn’t say, but he thought it probably had a lot to do with the merman who was sliding a finger inside of Castiel’s body. The intrusion felt odd and Cas was about to ask Dean to stop when the exploratory finger struck something unbelievable inside of him. His tail spasmed hard, shooting the both of them forward a few feet. 

Dean chuckled. “Found it.”

“What...?”

“Your joy buzzer,” smirked the other man. He began to rub it in small circles and Castiel’s nerves lit up like sea sparkles. It was pleasure unlike anything he’d ever felt and he could feel a mounting pressure. Trying to understand the sensation, he didn’t realize that Dean’s other hand had begun toying with his other slit, two inches below the first. Dean easily slipped a finger into his anus and began rubbing the organ from the other side as well. Cas thrashed in the water at the added stimulation.

“Yes!” babbled Castiel. “Yes, yes!!”

Realizing that Castiel was nearing his peak, Dean pulled his finger out of his lover’s top hole so he wouldn’t prevent the milt from escaping. Then he positioned Cas back over the pile of eggs and began tenderly fucking his asshole, pressing against the back side of his internal balls.

All of Castiel’s muscles contracted and his tail bowed. He sucked water through his gills in short gasps. And just when he thought he would snap, the tension crested and pleasure ran over him in great waves. White milt poured out of his hole, coating the eggs below. 

“Fuck,” muttered Dean, carefully pulling his finger out and thumbing alongside his own slit, “so fucking hot, Cas.”

With a heated stare, Castiel grabbed at Dean and pulled him in for another desperate kiss. He slid his hand down Dean’s deep red scales, intending to return the favor, but Dean caught his wrist. 

“Not here,” he grunted. “We’d fuck up the whole school.” Cas understood. A whole generation of fry not knowing who their clutch father was would be devastating.

“Come to my place?” Dean asked, his eyes begging. 

“Yes,” replied Castiel simply, tugging his new mate back toward the village to fully consummate their union. 

***

Three months later, Dean and Castiel found themselves at the nursery. They were watching as the fry played together. Ellen glanced at their joined hands.

“Well, you get first pick as the clutch daddy,” she said to Castiel. “You’ve got eight boys and five girls to choose from, each one strong and healthy. Who will it be?”

They gazed through the window again. Most of the fry had various shades of dark hair and scales in the blue or gray range, but the little boy with green scales stood out, as did the girl with red hair and a white tail with orange splotches. She was currently wrestling with one of her dark-haired brothers and giggling. 

“That hair is pretty distinctive,” said Dean, pointing her out. “Her mom’s got to be either Anna or Charlie.”

“Anna is my clutchmate,” Castiel explained. “She would not have laid eggs this time; the fry’s mother must be Charlie.”

Dean’s eyes lit up. “A fry from you and Charlie!”

“That one will keep you on your fins,” chuckled Ellen.

The toddler swam up to the nursery window, clumsy, but curious. As soon as Dean caught sight of her wide blue eyes, he squeezed Castiel’s hand. “That’s our girl,” he whispered.

Castiel squeezed back. “That’s our girl,” he agreed.

**Author's Note:**

> I've always wondered how merpeople have sex. In most of the fics I've read, the mermen have some kind of hidden penis, but I was never really satisfied by that. Why should mersex be just like human sex? But if it's not like human sex, what would it be like? This fic is my answer to that question, but I'd love to see some other creative interpretations!


End file.
